🎨 飞行侠完善 P1 功能：座位图 + @Agent + 会议纪要

新增功能:
- 座位可视化 - 圆形头像展示参会者
- @Agent 功能 - 定向消息给特定 Agent
- 会议纪要生成 - Web 界面一键生成
- 参会者列表 API

文件变更:
- meetings/views.py: mention_agent() 新接口
- templates/meeting_room.html:
  - 座位图 UI（圆形头像）
  - 生成纪要按钮
  - @Agent 按钮
- test_mention.py: @Agent 测试脚本

测试结果:
✅ 完整功能测试 (7 项)
✅ 会议纪要测试 (JSON + Markdown)
✅ @Agent 功能测试

backend/meetings/views.py

@@ -125,6 +125,70 @@ class MeetingViewSet(viewsets.ModelViewSet):
         serializer = ParticipantSerializer(participants, many=True)
         return Response(serializer.data)
     
+    @action(detail=True, methods=['post'])
+    def mention_agent(self, request, pk=None):
+        """@Agent 功能 - 发送消息给特定 Agent"""
+        meeting = self.get_object()
+        target_agent_id = request.data.get('target_agent_id')
+        content = request.data.get('content')
+        sender_agent_id = request.data.get('sender_agent_id')
+        sender_name = request.data.get('sender_name', 'User')
+        sender_emoji = request.data.get('sender_emoji', '👤')
+        
+        if not target_agent_id or not content:
+            return Response(
+                {'error': '缺少 target_agent_id 或 content'},
+                status=status.HTTP_400_BAD_REQUEST
+            )
+        
+        # 找到目标 Agent
+        target_participant = Participant.objects.filter(
+            meeting=meeting,
+            agent_id=target_agent_id,
+            left_at__isnull=True
+        ).first()
+        
+        if not target_participant:
+            return Response(
+                {'error': f'未找到 Agent: {target_agent_id}'},
+                status=status.HTTP_404_NOT_FOUND
+            )
+        
+        # 获取或创建发送者
+        sender_participant = Participant.objects.filter(
+            meeting=meeting,
+            agent_id=sender_agent_id,
+            left_at__isnull=True
+        ).first()
+        
+        if not sender_participant and sender_agent_id:
+            sender_participant = Participant.objects.create(
+                meeting=meeting,
+                agent_type='openclaw',
+                agent_id=sender_agent_id,
+                agent_name=sender_name,
+                agent_emoji=sender_emoji,
+                nickname=f"{sender_emoji} {sender_name}"
+            )
+        
+        if not sender_participant:
+            # 人类发送的，用主持人
+            sender_participant = Participant.objects.filter(
+                meeting=meeting,
+                is_host=True
+            ).first()
+        
+        # 创建消息，标记为需要回复
+        message = Message.objects.create(
+            meeting=meeting,
+            sender=sender_participant,
+            content=f"@{target_participant.nickname} {content}",
+            is_broadcast=False,  # 只发给目标 Agent
+            requires_response=True
+        )
+        
+        return Response(MessageSerializer(message).data, status=status.HTTP_201_CREATED)
+    
     @action(detail=True, methods=['get'])
     def messages(self, request, pk=None):
         """获取消息（人类轮询）"""